Can A Loose Oil Cap Cause Check Engine Light?

Many drivers need to pay more attention to the condition of the car’s oil cap; sometimes, after filling it, they forget to tighten it properly. This negligence seriously impacts your vehicle, including oil spills and loss of oil pressure. If the oil gets to other engine parts, it could damage them. You should pay much attention to the oil cap. Thus, can a loose oil cap cause check engine light?

Yes, a loose oil cap can trigger the check engine light, serving as a critical data point for car owners. This malfunction indicator lamp illuminates when the engine’s control software detects irregularities, including deviations in the crank case pressure data caused by a dislodged oil filler cap. Such a condition can lead to oil loss and affect engine performance.

Practice checking the engine oil level through the oil dipstick tube to guide maintenance actions. Visiting an auto repair shop allows drivers to consult a coach or technician, who uses an OBD reader to diagnose issues accurately. Ensuring the oil fill cap is secure can save money and prevent unnecessary trips to the shop, offering peace of mind and preserving the converter’s condition.

However, there may be other contributing factors. We’ve compiled a helpful guide on the implication of a loose cap and how it affects the vehicle. Also, answers to some frequently asked questions on this topic are provided.

can a loose oil cap cause check engine light

Can a loose oil cap cause check engine light?

Your engine light may come up if you have a loose oil cap. The oil cap works by sealing the oil reservoir completely. Prevent oil spills, loss of oil pressure, and contamination from entering the oil reservoir.

There are so many ways that a loose oil cap could cause the engine light to get triggered. The first is that the cap helps keep oil pressure in place. The oil pressure will escape through the engine oil cap when it is not tightened correctly. The oil pressure plays a huge role in the movement of oil through the engine block, and if there is not enough, many engine parts might not get oil, thereby triggering the check engine light.

Also, when you are driving car with a loose oil cap, the oil pressure will push the oil toward the oil cap, and you may experience shut off car due to oil leaking. However, this should not cause a check engine code, but the spilled oil could damage parts of the engine or and trigger an engine light.

What happens if oil cap is loose?

Many things could happen if your oil cap is loose. When this happens, it comes with loose oil cap symptoms. The symptoms are pretty easy to notice when driving; some can be seen sooner you open your vehicle’s hood.

Below are some of the bad oil cap symptoms.

1. Leaking oil

You will lose a lot of oil when driving with oil cap off or loosened. Oil pressure works with a lot of pressure that pushes the motor oil through the engine system. The pressure could quickly move the oil to the engine oil cap, making it spill. You can easily spot the leaking oil on the lid, around the engine, and on the ground.  

2. Loss of oil pressure

Another symptom is losing oil pressure. Since the cap is not tightened well enough, it is easy for oil pressure to escape. You can easily see this in the oil. To find the oil pressure, you can look at your dashboard, and beneath the indicator, you will see oil, or just H or L.

3. Oil Light

When you have a loosened oil cap, it will most likely trigger your oil light. It is because of the oil pressure and oil leaks that are happening. The light will come up when a significant amount of oil has leaked and the engine does not have enough oil left in the reservoir.

In some cases, the oil light could be accompanied by an engine light. When this happens, there might have been more significant damage done to the engine.

4. Smoke from the engine

Oil could get to the engine area due to the leaking oil. When this happens, the oil is burnt by the hot engine, and smoke from cap is released. A situation like this is most likely to happen with an oil cap missing.

It is essential to have the engine checked whenever you notice the loose oil cap symptoms. If you do not solve the problem, it could lead to a more serious problem. 

Will a loose oil cap cause a vacuum leak?

If you are driving with an oil cap off or lose, you will most likely have a vacuum leak. A vacuum leak is when air escapes into the intake system. The oil cap is designed to keep air and other contaminants from entering the engine system. It also keeps pressure in the engine system.

When the oil cap is loose or off, air can escape into the engine system. When this happens, it will disrupt the Air-fuel ratio, causing engine problems.

How to Check If Oil Cap Is Loose?

You do not need any particular method or steps to check if the oil cap is loose. All you have to do is open your vehicle’s hood and turn the oil cap. If the oil cap continues to move when you turn it, it needs to be tightened well.

People tend to make the mistake of tightening the oil cap properly. It is essential to ensure that your cap is tightened well before closing your hood. Tighten until you fill the final shift, which is quite noticeable.

You can also know our oil cap is loose through the earlier symptoms. When you notice the sign, you should check the oil cap to see if it is accurately tightened or has been damaged. If the cap is damaged, you will need to replace it.

Is bad oil cap is risky?

A bad oil cap is never a good sign for your vehicle and should be fixed as soon as possible.

Can too much oil damage engine?

If there is too much oil, it could affect the performance of the vehicle, therefore triggering a check engine light. Every vehicle has a specific oil capacity; when it goes beyond the oil capacity, it could expand when heated or spill into other engine parts and either contaminate or damage them entirely.

For instance, the oil could spill into the spark plug, contaminating it. Once this happens, the spark plug will not function as it should and may cause an engine misfire. When this goes on long enough, it will trigger the check engine light.

The overfilled oil could also affect other parts of the engine, like the crankshaft, allowing oil to escape into the combustion area and causing severe damage like engine clogging.

Will check engine light reset after tightening oil cap?

check engine light

Your engine light will turn off if you tighten the oil cap, when the cap causes the light. The light might turn off slowly, but the PCM should reset the engine light as you continue to drive.

However, if other underlying problems cause the engine light, then the light will not turn off. For instance, if the cap is damaged, the engine light will remain illuminated until you fix it. You replace the lid with a temporary oil cap or a permanent one.

Can you over tighten oil cap?

As much as the oil cap should be tightened correctly, you should not over-tighten it. By trying to over-tighten the cap, you can damage it. You can cause damage to the thread on the oil cap. Once the oil cap is damaged, then spaces for oil pressure and oil to escape from are created.

How tight should the engine oil cap be?

Your oil cap must be fitted and tightened properly; if it is not done properly, it may be damaged or stripped. If this happens, you need to replace the oil cap immediately.

engine oil cap

People have complained that the oil cap came off while driving, and what can I use as a temporary oil cap? When you experience a damaged oil cap that keeps coming off while driving, you can use duct tape to seal it. It is not a permanent solution as you still need to get a new oil cap, but this will take you to where you will get a new cap.


Hopefully, you are clear about the question, can a loose oil cap cause check engine light? You will lose a lot of oil if you attempt to move without the cap or a loose filler cap. Your oil will go spraying out of the vehicle and may cause severe damage to other parts of the engine.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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